Connected: An Internet Encyclopedia
NFS Protocol Overview

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### NFS Protocol Overview

The Network File System (NFS), developed by Sun Microsystems, is the defacto standard for file sharing among UN*X hosts. NFS Version 3 is documented in RFC 1813. The Mount Protocol is closely related.

NFS is implemented using the RPC Protocol, designed to support remote procedure calls. All NFS operations are implemented as RPC procedures. A summary of NFS procedures is show below:

    Procedure 0:  NULL - Do nothing
    Procedure 1:  GETATTR - Get file attributes
    Procedure 2:  SETATTR - Set file attributes
    Procedure 3:  LOOKUP - Lookup filename
    Procedure 4:  ACCESS - Check Access Permission
    Procedure 5:  READLINK - Read from symbolic link
    Procedure 6:  READ - Read From file
    Procedure 7:  WRITE - Write to file
    Procedure 8:  CREATE - Create a file
    Procedure 9:  MKDIR - Create a directory
    Procedure 10: SYMLINK - Create a symbolic link
    Procedure 11: MKNOD - Create a special device
    Procedure 12: REMOVE - Remove a File
    Procedure 13: RMDIR - Remove a Directory
    Procedure 14: RENAME - Rename a File or Directory
    Procedure 15: LINK - Create Link to an object
    Procedure 16: READDIR - Read From Directory
    Procedure 17: READDIRPLUS - Extended read from directory
    Procedure 18: FSSTAT - Get dynamic file system information
    Procedure 19: FSINFO - Get static file system Information
    Procedure 20: PATHCONF - Retrieve POSIX information
    Procedure 21: COMMIT - Commit cached data on a server to stable storage

NFS is a stateless protocol. This means that the file server stores no per-client information, and there are no NFS "connections". For example, NFS has no operation to open a file, since this would require the server to store state information (that a file is open; what its file descriptor is; the next byte to read; etc). Instead, NFS supports a Lookup procedure, which converts a filename into a file handle. This file handle is an unique, immutable identifier, usually an i-node number, or disk block address. NFS does have a Read procedure, but the client must specify a file handle and starting offset for every call to Read. Two identical calls to Read will yield the exact same results. If the client wants to read further in the file, it must call Read with a larger offset.

Of course, this is seldom seen by the end user. Most operating systems provide system calls to open files, and read from them sequentially. The client's operating system must maintain the required state information, and translate system calls into stateless NFS operations.

#### NFS Performance

NFS performance is closely related to RPC performance. Since RPC is a request-reply protocol, it exhibits very poor performance over wide area networks. NFS performs best on fast LANs.

Connected: An Internet Encyclopedia
NFS Protocol Overview